Mechanical Memory in Plants: Insights from Mimosa pudica

Plants provide a unique and experimentally amenable arena for studying the dynamics of information storage and transfer in a complex system. Mimosa pudica, or the "sensitive plant", possesses small leaflets that fold in response to touch, rapid temperature changes, and electrical stimulation, making it a desirable model plant for probing the mechanical storage and propagation of information. This behavior comes at a tradeoff, as it serves as a defense mechanism to deter herbivores, but reduces the plant's ability to photosynthesize. After being repeatedly exposed to non-damaging stimuli, the plants only partially close their leaves, if at all, and reopen them more quickly. However, the mechanism by which plants are able to store such "mechanical memory" is currently unclear. We perform a behavioral assay on Mimosa pudica plants using a controllable electrical stimulation setup to investigate how the plants' leaf-folding response varies with stimulation intensity and frequency. We use experimental observations to fit a mathematical model of leaf-folding dynamics that incorporates memory by integrating over the temporal history of stimuli. Ultimately, our results translate the behavioral and mechanical principles of Mimosa pudica to inform the design of biomimetic materials and robotic systems that can retain and retrieve mechanical memory.